This invention relates to a hydraulic circuit for a hydraulically driven vehicle and in particular to such a hydraulic circuit provided with a straight run compensator valve.
A hydraulically driven vehicle is generally provided with a pair of independent hydrostatic transmissions of a closed loop, each for driving one side of undercarriages. Each closed loop includes a variable displacement hydraulic pump driven by an engine and a hydraulic motor driven by the variable displacement hydraulic pump. Displacement volume of each variable displacement hydraulic pump is controlled by respective servo controls.
While a vehicle is running straight, theoretically both variable displacement hydraulic pumps deliver the same amount of fluid. However, this is not always true in practical sense and each variable displacement pump deliver a slightly different amount of fluid from each other resulting in different fluid pressure in respective closed loops. Besides, loads applied on respective undercarriages are different from each other causing a different fluid pressure in the respective closed loops. Accordingly, the vehicle is apt to turn right or left slightly even if it is set to run straight because respective hydraulic motors is rotated in different speed from each other in such occasions.